This invention relates generally to the cooling of electronic and optical devices. More specifically, the invention relates to an impingement cooling device for a diode pumped laser slab that uses a fluorescent energy absorbing material to cool the laser slab.
Generally, a diode pumped laser is a solid state laser constructed from a semi-conductor material. A voltage is applied across the semi-conductor and causes the emission of light radiation.
Traditionally, diode pumped laser slabs have included bonded layers of dissimilar materials, such as yttrium-aluminum-garnet (YAG) bonded with sapphire. For the laser to function correctly, the bonded interface must maintain a low stress level.
Diode lasers typically operate intermittently such as cycling between two seconds on and two seconds off. This cycling operation produces heat and stray fluorescent light. The stray fluorescent light reflects back to the slab and dissipates as heat. Poor dissipation of the heat creates thermal stresses at the bonded interface and can cause the laser to malfunction. To avoid this potential problem, the temperature of the bonded interface must be maintained at an isothermality of 5° C. or lower.
One method for managing and dissipating the heat utilizes a heat exchanging device, such as an impingement cooling device. An impingement cooling device includes a series of stacked layers with each layer being positioned approximately parallel to the laser slab. The layers contain fluid channels (spacers) and fluid orifices such that when the layers are stacked, the channels and orifices form pathways through the stack leading to and from the laser slab. A coolant circulates through pathways formed by sets of orifice and spacer layers to impinge onto the laser slab and then exits through relatively straight fluid channels.
Conventional impingement cooling devices, such as those produced of copper layers, do not adequately manage stray fluorescent light. Conventional devices reflect the stray fluorescent light back into the laser slab. Thus, the laser slab generates additional heat from the absorption of the stray fluorescent light, thereby concentrating the total heat generated by the laser slab at the cooler-slab interface. This increased heat concentration makes it more difficult to maintain a proper temperature in the laser slab.
Additionally, conventional impingement cooling devices do not have adequate heat dissipation characteristics. In such conventional devices, the copper layer closest to the laser slab absorbs heat from the laser slab. Thus, the copper layer closest to the laser slab has a relatively high heat absorption density compared to copper layers that are positioned farther from the laser slab. This uneven heat absorption density further adds to the difficulty of maintaining a proper temperature in the laser slab.
Thus, there is a need for a cooling device that provides improved management of stray fluorescent light and improved heat dissipation characteristics.